2025 Component Abuse Challenge: Conductive Filament Makes A Meltable Fuse

October 19, 2025 by Donald Papp 12 Comments

Everything is a fuse if you run enough current through it. Or at least [JohnsonFarms.us] seems to think so, which has led him to design 3D-printed fuses made from conductive PLA filament.

Conductive filament is a meltable resistor, which, if one squints hard enough, is basically a fuse.

In theory a 3D printed fuse works the same as a normal one: excessive current draw will cause the conductive plastic to briefly become a heater, causing it to self-destruct and break the electrical connection. There’s a risk of melted plastic and perhaps a nonzero combustion risk, but [JohnsonFarms.us] is less interested in whether this is a good idea and more interested in whether it can work at all, and with what degree of predictability and/or regret.

His experiments so far show that printed fuses are essentially meltable resistors with values between 300 Ω and 1250 Ω, depending on shape. What it takes to bring those to roughly 60 °C, where PLA softens, and around 150 °C, where PLA melts, is next on the to-do list.

Whatever conclusions are reached, it is interesting to think of conductive filament as a meltable resistor, and ponder what unusual applications that might allow.

Most conductive filaments have high resistance, but not all. Some, like Electrifi by Multi3D, have extremely low resistance and were used in a project that made 3d-printed logic gates.

2025 Component Abuse Challenge: Boosting Voltage With Just A Wire

October 17, 2025 by Jenny List 13 Comments

Switching power supplies are familiar to Hackaday readers, whether they have a fairly conventional transformer, are a buck, a boost, or a flyback design. There’s nearly always an inductor involved, whose rapid change in magnetic flux is harnessed to do voltage magic. [Craig D] has made a switching voltage booster that doesn’t use an inductor, instead it’s using a length of conductor, and no, it’s not using the inductance of that conductor as a store of magnetic flux.

Instead it’s making clever use of reflected short pulses in a transmission line for its operation. Electronics students learn all about this in an experiment in which they fire pulses down a length of coax cable and observe their reflections on an oscilloscope, and his circuit is very similar but with careful selection of pulse timing. The idea is that instead of reflected pulses canceling out, they arrive back at the start of the conductor just in time to meet a pulse transition. This causes them to add rather than subtract, and the resulting higher voltage pulse sets off down the conductor again to repeat the process. We can understand the description, but this is evidently one to sit down at the bench and experiment with to fully get to grips with.

Continue reading “2025 Component Abuse Challenge: Boosting Voltage With Just A Wire” →

2025 Component Abuse Challenge: An LED As A Light Dependent Capacitor

October 16, 2025 by Jenny List 15 Comments

The function of an LED is to emit light when the device is forward biased within its operating range, and it’s known by most people that an LED can also operate as a photodiode. Perhaps some readers are also aware that a reverse biased LED also has a significant capacitance, to the extent that they can be used in some RF circuits in the place of a varicap diode. But how do those two unintentional properties of an LED collide? As it turns out, an LED can also behave as a light dependent capacitor. [Bornach] has done just that, and created a light dependent sawtooth oscillator.

The idea is simple enough, there is a capacitance between the two sides of the depletion zone in a reverse biased diode, and since an LED is designed such that its junction is exposed to the external light, any photons which hit it will change the charge on the junction. Since the size of the depletion zone and thus the capacitance is dependent on the voltage and thus the charge, incoming light can thus change the capacitance.

The circuit is a straightforward enough sawtooth oscillator using an op-amp with a diode in its feedback loop, but where we might expect to find a capacitor to ground on the input, we find our reverse biased LED. The video below the break shows it in operation, and it certainly works. There’s an interesting point here in that and LED in this mode is suggested as an alternative to a cadmium sulphide LDR, and it’s certainly quicker responding. We feel duty bound to remind readers that using the LED as a photodiode instead is likely to be a bit simpler.

This project is part of the Hackaday Component Abuse Challenge, in which competitors take humble parts and push them into applications they were never intended for. You still have time to submit your own work, so give it a go!

Continue reading “2025 Component Abuse Challenge: An LED As A Light Dependent Capacitor” →

How Bad Can A Cheap Knockoff ADS1115 ADC Be?

October 15, 2025 by Maya Posch 29 Comments

Although the saying of caveat emptor rings loudly in the mind of any purveyor of electronic components, the lure of Very Cheap Stuff is almost impossible to resist. Sure, that $0.60 Ti ADS1115 ADC on LCSC feels like it almost has to be a knock-off since the same part on Digikey is $4 a pop, and that’s when you buy a pack of 1,000. Yet what if it’s a really good knockoff that provides similar performance for a fraction of the price, such as with those cheap ADC boards you can get from Amazon? Cue [James Bowman] letting curiosity getting the better of him and ordering a stash of four boards presumably equipped with at least some kind of cheapo knockoff part, mostly on account of getting all boards for a mere $2.97.

The goal was of course to subject these four purported ADS1115s to some testing and comparison with the listed performance in the Ti datasheet. Telling was that each of the ADCs on the boards showed different characteristics, noticeably with the Data Rate. This is supposed to be ±10% of the nominal, so 7.2 – 8.8 times per second in 8 samples per second mode, but three boards lagged at 6.5 – 7 SPS and the fourth did an astounding 300 SPS, which would give you pretty noisy results.

Using a calibrated 2.5 voltage source the accuracy of the measurements were also validated, which showed them to be too low by 12 mV. The good news was that a linear correction on the MCU can correct for this, but it shows that despite these parts being ADS1115 compatible and having features like the PGA working, you’re definitely getting dinged on performance and accuracy.

[James] said that he’s going to run the same tests on an ADS1115 board obtained from Adafruit, which likely will have the genuine part. We would also love to see someone test the $0.60 version from LCSC to see whether they can match the datasheet. Either way, if you are eyeing this ADC for your own projects, it pays to consider whether the compromises and potential broken-ness of the knockoffs are worth it over coughing up a bit more cash. As they say, caveat emptor.

The Texas Instruments branding with some schematic symbols in background.

More Than 100 Sub-Circuit Designs From Texas Instruments

October 15, 2025 by John Elliot V 18 Comments

We were recently tipped off to quite a resource — on the Texas Instruments website, there’s a page where you can view and download a compendium of analog sub-circuits.

Individual circuits can be downloaded in the form of PDF files. If you chose to register (which is free), you’ll also gain access to the pair of e-books listed at the bottom of the page: Analog Engineer’s Circuit Cookbook: Amplifiers and Analog Engineer’s Circuit Cookbook: Data Converters. The data converter circuits can be further subdivided into analog-to-digital converter (ADC) circuits and digital-to-analog converter (DAC) circuits.

There are more than 60 amplifier circuits including basic circuits, current sensing circuits, signal sources, current sources, filters, non-linear circuits (rectifiers/clamps/peak detectors), signal conditioning, comparators, sensor acquisition, audio, and integrated amplifier circuits using MSP430 microcontrollers.

You’ll also find 39 analog-to-digital converter (ADC) circuits including low-power, small size, and cost optimized circuits; level translation and input drive circuits; low-level sensor input circuits; input protection, filtering and isolation circuits; and commonly used auxiliary circuits. Finally, there are 15 digital-to-analog converter (DAC) circuits including audio outputs, auxiliary and biasing circuits, current sources, and voltage sources.

Thanks to [Lee Leduc] for letting us know over on the EEVblog Forum.

2025 Component Abuse Challenge: Making A TTL Demultiplexer Sweat

October 14, 2025 by Jenny List 6 Comments

When we think of a motor controller it’s usual to imagine power electronics, and a consequent dent in the wallet when it’s time to order the parts. But that doesn’t always have to be the case, as it turns out that there are many ways to control a motor. [Bram] did it with a surprising part, a 74ACT139 dual 4-line demultiplexer.

A motor controller is little more than a set of switches between the supply rails and the motor terminals, and thus how it performs depends on a few factors such as how fast it can be switched, how much current it can pass, and how susceptible it is to any back EMF or other electrical junk produced by the motor.

In this particular application the motor was a tiny component in a BEAM robot, so the unexpected TTL motor controller could handle it. The original hack was done a few decades ago and it appears to have become a popular hack in the BEAM community.

Inside A Germanium Transistor

October 10, 2025 by Jenny List 9 Comments

The first transistors were point contact devices, not far from the cats-whiskers of early radio receivers. They were fragile and expensive, and their performance was not very high. The transistor which brought the devices to a mass audience through the 1950s and 1960s was the one which followed, the alloy diffusion type. [Play With Junk] has a failed OC71 PNP alloy diffusion transistor, first introduced in 1957, and has cracked it open for a closer look.

Inside the glass tube is a small wafer of germanium crystal, surrounded by silicone grease. It forms the N-type base of the device, with the collector and emitter being small indium beads fused into the germanium. The junctions were formed by the resulting region of germanium/indium alloy. The outside of the tube is pained black because the device is light-sensitive, indeed a version of this transistor without the paint was sold as the OCP71 phototransistor.

These devices were leaky and noisy, with a low maximum frequency and low gain. But they were reliable and eventually affordable, so some of us even cut our electronic teeth on them.

Continue reading “Inside A Germanium Transistor” →